Nitro dyes, especially 2-nitroaniline derivatives, have long been used in the hair coloring art, including both oxidative and nonoxidative hair dye compositions. Such compositions typically include two or more hair dyes to provide an acceptable composite coloring effect to the hair. Depending on the shade desired, more or less of a yellow hair dye would be included. Indeed, in the dyeing of hair with a direct dye, it is necessary to provide dyes in admixture, to produce the natural shades desired. Yellow dyes are especially useful to impart blond and other lighter shade to human hair.
A direct yellow dye of the prior art that is characterized by color fastness in the absence of light is: ##STR3## which compound is described in U.S. Pat. Nos. 4,337,061 and 4,417,896. Disadvantageously, the compound (II) has less than desirable light stability.
EP 182,330 discloses the direct dye: ##STR4## wherein R.sup.1 and R.sup.2 stand for H, C.sub.1 -C.sub.4 alkyl, C.sub.2 -C.sub.4 monohydroxyalkyl and C.sub.3 -C.sub.4 dihydroxyalkyl, except that R.sup.1 and R.sup.2 do not simultaneously stand for C.sub.1 -C.sub.4 alkyl radicals, and X is one of the radicals alkyl, monohydroxyalkyl, perfluoralkyl or halogen. Upon variation of the substituent X, the compound provides yellow shades ranging from blue-tinged lemon yellow to pure yellow to orange. Unfortunately, compounds represented by formula III, especially when R.sup.1 is CH.sub.2 CH.sub.2 OH; R.sup.2 is hydrogen, and X is CF.sub.3 have a lower affinity for hair than compounds of formula I when R.sub.1 is CH.sub.2 CH.sub.2 OH, and R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are all hydrogen. Accordingly, a greater amount of the aforementioned Compound (III) is needed to obtain an equivalent color on hair.
U.S. Pat. No. 4,619,666 describes hair coloring preparations containing as hair dyes, compounds typically of the formula: ##STR5## including 4-(2-hydroxyethylamino)-3-nitrobenzoic acid and several additional homologs and analogs of that compound in which R may be hydrogen, C.sub.1 -C.sub.4 alkyl and a number of other substituents. These compounds contain anionic groups which gives them a poor affinity for hair under typical alkaline dyeing conditions.
Copending and commonly owned U.S. application Ser. No. 07/333,528 discloses and claims hair dyes of the formula: ##STR6## wherein R.sub.1 and R.sub.2, R.sub.3 which may be identical or different, are hydrogen, alkyl, hydroxyalkyl, polyhydroxyalkyl, alkoxyalkyl, hydroxyalkoxyalkyl, aminoalkyl and dialkylaminoalkyl, each alkyl group and each alkoxy group having from about 1 to about 6 carbons, and R.sub.3 is a compatible substituent group, for example, hydrogen, alkyl having from about 1 to about 6 carbon atoms and halogen. These compounds, however, may slowly hydrolyze in alkaline formulations. The compounds utilized in the compositions of this invention are not subject to such hydrolysis.